MichaelBluejay - 5:30 pm on Oct 3, 2012 (gmt 0)

I'm trying to pull the most recent posts out of a table, but have each topic represented only once.

This gets the posts, but takes more than one from each topic:

SELECT topic_id,posted,poster,message FROM posts ORDER BY posted DESC LIMIT 20

Adding a GROUP BY makes sure each thread is represented only once, but then I no longer get the most recent post from each topic:

SELECT topic_id,posted,poster,message FROM posts GROUP BY topic_id ORDER BY posted DESC LIMIT 20

I tried to put "ORDER BY" before "GROUP BY", but that just gives me a syntax error:

SELECT topic_id,posted,poster,message FROM posts ORDER BY posted DESC LIMIT 20[ GROUP BY topic_id

How should I write my query?